Theoretical approaches are being developed to extract information concerning the nature of internal motions in a variety of biopolymers from nuclear magnetic relaxation and time-resolved fluorescence depolarization experiments. It has been shown that multinuclear relaxation results on DNA imply the existence of large amplitude internal motions on the nanosecond time scale. In addition, a new method for calculating diffusion-controlled association rates of ligand binding to macromolecules has been developed. The influence of rotational diffusion and orientation constraints on such rates has been quantitatively determined.